Ch. 44 Osmoregulation and Excretion

A Balancing Act

FYI

Diabetes facts •The prevalence of diabetes type II has reached epidemic proportions.

•An estimated 285 million people, corresponding to 6.4% of the world's adult population, will live with diabetes in 2010.

•WHO predicts that developing countries will bear the brunt of this epidemic in the 21st century. Currently, more than 70% of people with diabetes live in low- and middle income countries.

44.1 An animals nitrogenous waste reflect its evolution and its habitat

1. Metabolic wastes must be dissolved in water, so type and quantity of waste will impact water balance.

2. As protein and nucleic acids are broken down. NH3 Ammonia forms.

3. Ammonia= toxic=death

4. Some animals excrete NH3 directly others convert it into a less toxic molecule

5. Urea-nontoxic, uses less water but requires ATP. Produced in the liver.

6. Uric Acid-semisolid paste, nontoxic, less water but lots of ATP

44.3 Diverse excretory systems are variations on a tubular themeKey Function: produce a filtrate by pressure-filtering and then modify the filtrate’s content

1. Filtration- tubule collect filtrate from blood. Water and solutes are forced by blood pressure across the SPM of a cluster of capillaries into tubule

2. Reabsorbtion –Transport epithelium reclaims valuable substances and returns them to body fluids.

3. Secretion- Other substances , (toxins, excess ions) are extracted from the body fluids

4. Excretion-The filtrate leaves the system and the body

44.4 Nephrons/assoc. blood vessels are the functional units of the kidneys

1.Proximal Tubule= reabsorption and secretion. H+, NH3, drugs and poison into the filtrate. Glucose, amino acids. K+, bicarbonate, are actively or passively reabsorbed into the blood.

2. D. loop of Henle= permeable to water only. The interstitial fluid is increasingly hyperosmotic toward the inner medulla. So water exits by osmosis leaving behind a filtrate with high solute concentration

3. A. Loop of Henle= Permeable to salt only, which diffuses out of the lower thin layer segment of the loop, increasing the osmolarity of the medulla.NACL is actively transported out of the thick segment. As salt leaves the filtrate becomes less concentrated.

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4. The distal tubule= regulates K+ secretion into the filtrate and NACL reabsorption into the cortex, it helps to regulate pH by secreting H+ and reabsorbing bicarbonate

5. As the filtrate moves in the collecting through the osmotic gradient of the medulla, more and more water exits by osmosis.

Urea diffuses out of the lower portion of the duct and helps to maintain the osmotic gradient.

Salt excretion is controlled by the transport epithelium actively reabsorbing NACL

44.5 Water conservation is essential to life on landThe counter current multiplier system: Using Energy to create concentration gradients.

The CCMS in the loop of henle maintains high salt concentration in the interior of the kidney, enabling the kidney to form concentrated urine.

Negative feedback loop involved in controlling the osmolarity of the blood.Human Set point 300mosm/L

Increase in Osmolarity means more salt less water. ( Water loss or ingestion of salty food)

Decrease means more water less salt.(Large in take of water)

Remember that the goal is to stay within very close range of the set point.